NO179856B - Method for removing or reducing hydrogen sulfide content in hydrocarbons or water - Google Patents

Description

The present invention relates to the removal or reduction of hydrogen sulphide in hydrocarbons or water. In particular, the present invention relates to such removal or reduction by chemical means.

When drilling, producing, transporting, storing and processing crude oil, including waste water in connection with crude oil production, and when storing residual fuel oil, you often come across hydrogen sulphide, which is a highly toxic substance. Also at the head of the oil well, vapors containing hydrogen sulphide are released from light hydrocarbons which must be kept under control. Uncontrolled release of hydrogen sulphide can have serious health consequences. Combustion of such vapors neither solves the toxic gas problem nor is it economical, as the light hydrocarbons have considerable value. Hydrogen sulphide is also often present in the underground water that is removed together with the crude oil, in the crude oil itself and in gases that occur in connection with such water and oil. When water and oil are separated from each other using separation tanks, de-emulsifiers and the like, intolerable quantities of hydrogen sulphide are given off in the form of a gas together with water and hydrocarbon vapours. Natural gases are often acidic, i.e. they contain some hydrogen sulphides.

According to the present invention, liquid hydrocarbons containing hydrogen sulphide, as well as hydrocarbon gases, such as natural gas or exhaust gases from the production, transport, storage and refining of crude oil, can be controlled in a convenient, easy and economical way.

In short, the present invention is therefore aimed at a method for breaking down hydrogen sulphide in an aqueous medium and/or a hydrocarbon medium. According to this method, the medium is contacted with an effective amount of an amidine selected from the group consisting of monoamidines with from 1 to about 18 carbon atoms and polyamides comprising from 2 to 3 amidine groups with from 1 to approx. 18 carbon atoms per amidine group.

Among the many advantages of the invention can therefore be mentioned the provision of an improved method for removing hydrogen sulphide from a hydrocarbon medium and/or an aqueous medium, as well as the provision of such a method which can be used for widely different media of this type.

NO A 870 351 describes a method for removing hydrogen sulphide from crude oil using a compound with the formula

where X and Y are carbon or nitrogen atoms. Within this formula one can indeed get an amidine functionality, but it is here that the electronegative groups are decisive, and the double bond of the amidine function is not important.

According to the present invention, it has been discovered that if an aqueous medium and/or a hydrocarbon medium is brought into contact with certain amidines, a highly effective technique for breaking down the hydrogen sulphide in the medium is provided. Both polyamides and monoamidines have been found to be effective.

Monoamidines which have been found to be particularly effective in the present process for removing hydrogen sulfide correspond to the formula

where R, R<1>, R<2> and R<3> are independently selected from H, alkyl groups with up to approx. 18 carbon atoms and aryl groups with up to approx. 18 carbon atoms, and where R<4> is an alkylene group with up to approx. 18 carbon atoms, with the proviso that the total number of carbon atoms in R, R<1>, R<2>, R<3> and R<4> is from 1 to approx. 18. The alkyl, aryl and alkylene groups can be substituted or unsubstituted, branched or straight chain.

In general, it is desirable to maintain a partial positive charge on the central carbon atom; i.e. the carbon between the two nitrogens. Preferred radical groups thus maintain or increase the positive charge on this central carbon atom. In this regard, it has been found that it is preferred that R1 is hydrogen or, more preferably, an aryl group, especially an aryl group substituted with an electron-withdrawing group, such as a nitro, cyano or halide group.

In addition, it is desirable to maintain the basicity that the nitrogen imparts to the mixtures. Cycloalkyl or especially hydrogen or a lower alkyl group is thus more desirable than phenyl for R, R<2> and R<3>. Any of R, R<1>, R<2> and R<3> may be substituted or unsubstituted alkyl or aryl groups. Heteroatoms, such as oxygen, sulfur and nitrogen, are suitable substituents. Likewise, R<4> can be a substituted or unsubstituted alkylene or arylene group. If liquid media are to be treated, R, R<1>, R<2>, R<3> and R<4> should be chosen so that the amidine is soluble in the medium to be treated to such an extent that a hydrogen sulfide-destroying amount of the amidine can be thoroughly mixed into the medium.

In general, therefore, the hydrogen sulfide-destroying effectiveness of amidine mixtures with higher pKa values has typically been found to be higher than for amidine mixtures with lower pKa values. In reality, highly acidic mixtures may show a tendency to react to form inactive salts when added to a medium to be treated. Amidines with pKa = 7 or higher, especially approx. 10 or higher, such as a cyclic amidine, where the ring has 6 parts (e.g. tetrahydropyrimidine), is therefore preferred. Accordingly, cyclic groups have been found to be particularly desirable for R, R<2> and R<3> and alkanolamines have also been found to give excellent results. For amidines that will provide an acidic environment, a buffer can be added to the mixture to raise the pH value.

Polyamidines, such as those corresponding to the formulas

A^R5-^2 or

is also suitable for use in the present method. In such formulas, the amidine groups A<1>, A<2> and A<3> are chosen independently among

where R, R1, R<2> and R<3> for each of A1, A<2> and A<3> are independently selected from H, alkyl groups of up to 18 carbon atoms and aryl groups of up to 18 carbon atoms, and R< 4> for each of A<1>, A<2> and A<3> is independently selected from among alkylene groups of up to 18 carbon atoms, provided that the total number of carbon atoms in R<1>, R<2>, R <3> and R<4> per A is from 1 to approx. 18; R<5 >is an alkylene group with up to approx. 8 carbon atoms or an arylene group with up to approx. 8 carbon atoms, and R<6> is an alkylene group with up to approx. 8 carbon atoms or an arylene group with up to approx. 8 carbon atoms. As with the monoamidines, any of the alkyl, aryl, alkylene and arylene groups may be substituted or unsubstituted, branched or straight chain.

The same considerations that were taken in the selection of R-'-, R<2>, R<3> and R<4> can be applied to polyamides, as discussed in the case of monoamidines. It is thus desirable to select groups which maintain or increase the positive charge on the central carbon to give a basic mixture. Preferably it is from approx. 2 to approx. 6 carbon atoms between the amidine groups. R^ and R<*>> may contain heteroatoms and may be straight-chained or branched. Cyclic groups and alkanolamines are particularly desirable substituents for R<1>, R<3> and R<4>.

The amidines that can be used in the method according to this invention can be synthesized using several known techniques. For example, US Patent No. 4,321,202 describes methods for preparing such amidines. Likewise, methods for the preparation of amidines are described in Taylor and Ehrhart, "A Convenient Synthesis of N,N'-disubstituted Form Amidines and Acid Amidines", Journal of Organic Chemistry, vol. 28, pp. 1108-1112, April 1963 , and Synthesis, Jan. 1983, pp. 36-37.

When using, add from approx. 10 ppm to approx. 500 ppm of the amidine according to this invention to an aqueous medium and/or a carbon medium. The amidine is effective in many different media. The amidine is thus not only usable in an aqueous medium, but also in many different hydrocarbon media, e.g. hydrocarbon distillate products, such as diesel fuel, gasoline, kerosene, light cycle oil, light cycle gas oil, vacuum gas oil and even crude oil and residual products. If the medium is a residual product, the amidine can be added by adding a small amount of mixture components containing the amidine. In cases where the medium is a vapour, the amidine can be added by atomizing the amidine in a pipeline.

The following examples illustrate the invention.

Example I

N-methylformamide (15 g) was placed in a 200 ml round bottom flask containing toluene (10 ml). Dimethylcarbamyl chloride (27 g) was added in portions, and the sample was refluxed for approx. 1 hour. To begin with, a strong release of carbon dioxide took place. The reflux was interrupted when the release of carbon dioxide ceased. The sample was then cooled to ambient conditions and the toluene stripped off in a rotary evaporator. What remained was a pale yellow solid. This solid (amidine-HCl) was dissolved in chloroform (ca. 70 mL) and added to a solution of 50% aqueous sodium hydroxide (25

g) and distilled water (20 ml). The sample was well stirred and allowed to separate. The chloroform layer was taken out and filtered. Another one

aliquot of chloroform (20 ml) was added, stirred and separated. The two extracts were combined and the mixture was distilled at 760 torr. Fractions were taken as follows: F1 at 61°C; F2 at 64 - 70°C; F3 at 70 - 78°C; F4 at 80 - 90°C, F5 at 90 - 97°C and F6 at 97 - 102°C. Fraction 4 contained the desired product, although the boiling point for pure product according to the literature is 106°C at 730 torr.

Example II

Acetic acid (15 g) and triethyl orthoformate (37 g) were mixed and heated to approx. 100°C. Ethylamine (32.1 g of 70% by weight aqueous solution) was added dropwise and the resulting mixture was heated under reflux for 2 hours. The apparatus was fitted with a Dean Stark trap and volatile material (0.53 ml) was removed by distillation. The distillation was interrupted when the temperature in the container reached 145°C. The mixture was then cooled and dichloromethane (50 g) was added. The resulting mixture was then added to a mixture of sodium carbonate (50 g) and distilled water (350 ml), stirred for 5 minutes and then transferred to a separatory funnel. The organic layer was pulled off and the solvent was evaporated on a rotary evaporator at 50°C with a suction device. NMR analysis showed that the product was impure and that it contained traces of acetic acid and possibly amide acid salt. The dividend was calculated at 4.8%.

Example III

Acetic acid (6 g) and triethyl orthoacetate (16.2 g) were; mixed and ethylamine (12.9 g of 70% aqueous solution) was added dropwise. A round bottom flask was fitted with a condenser to prevent loss of ethylamine. The mixture was then refluxed for 2 hours at 80°C. The volatile material was allowed to distill off and into a Dean Stark trap. The sample was boiled under reflux at a temperature in the flask of 140°C. 21 ml of the material was withdrawn and the mixture was cooled overnight. The material was then diluted with methylene chloride (50 mL). The resulting solution was then poured into water (250 ml) containing sodium carbonate (50 g). The pH value of the water after extraction was measured to be 11. The mixture was then transferred to a separatory funnel and allowed to separate. The underlying organic phase was withdrawn and potassium hydroxide pellets (about 5 g) were added to absorb residual water and to complete neutralization of the amidine acetate. After filtration, the rest of the liquid was distilled at 65 torr. About. 1 ml of the liquid was back. Analysis of this liquid showed contamination.

Example IV

A mixture of ethyl orthoformate (34 g) and acetic acid (13.8 g) was heated to reflux (about 100°C). Amine [CH 3 (CH 2 ) 3 NH 2 , 33.6 g] was quickly added. The mixture was refluxed for 2 hours. The apparatus was then fitted with a Dean Stark trap and volatile material (about 40 ml) was removed until the temperature in the flask rapidly rose to 160°C. The sample was then cooled and shaken in a separatory funnel with ether and water (300 ml) containing sodium carbonate (50 g). Three teams formed and separated from each other. Each layer was left in a beaker overnight to allow the ether to evaporate. About. 25 mL of each layer remained and they were all combined and distilled at 0.9 torr. Two fractions were taken, one at 85°C and 0.9 torr (3.05 g) and the other at 90°C and 0.9 torr (4.13 g). These fractions showed a mixture of amidine and amide, possibly acetal and formamide.

Example V

The amidine according to example IV was also prepared as follows: A mixture of acetic acid (13.8 g) and ethyl orthoformate (34 g) was heated to reflux (approx. 100°C). Amine [33.6 g CH3(CH2)3NH2] was quickly added using an addition funnel. The mixture was then refluxed for 2 hours and then stood over the weekend, after which it was fitted with a Dean Stark trap and volatiles were collected (about 40 ml theoretical). Ethanol (35 mL) was removed. The temperature in the flask rose to 160°C. The amber viscous liquid was mixed with ether (200 mL) and 10% caustic/water (10 mL) was added to the ether mixture to convert the amidine acetate to free amidine and the water was drawn off. The pH value in the water was 11. The ether mixture was evaporated on a rotary evaporator and there remained approx. 4 0 ml viscous amber liquid. This part was distilled, one fraction being taken out at 80°C and 0.7 torr. A water-white, slightly viscous liquid was produced. NMR spectroscopy confirmed the amidine structure of the product.

Example VI

Ethyl orthoformate (17 g) was heated to approx. 100°C and benzylamine (24.6 g) was quickly added. The mixture was heated to reflux. When the temperature in the flask reached approx. 140°C, what appeared to be ethanol began to distill off. About. 11 mL of liquid distilled into a Dean Stark trap. The distillation was interrupted when the temperature in the flask reached approx. 150°C. Crystals formed which were purified by recrystallization in hexane. A dividend of approx. 52%.

Example VII

Triethyl orthoformate (17 g) was placed in a 250 ml round bottom flask and heated to approx. 100°C. Ethanolamine (14 g) was added at once and the mixture was refluxed for 8 hours, until the reflux amounted to 20 ml of ethanol. NMR analysis of the product at this point showed an impurity and the mixture was then distilled under vacuum and one fraction withdrawn at 70-75°C and 20 torr. A dividend of approx. 50% was calculated.

Example VIII

Triethyl orthoformate (17 g) was placed in a round bottom flask and heated to approx. 100°C. Diethylenetriamine (47.5 g) was added in one portion and the mixture was refluxed for several hours at approx. 140°C before any liquid was detected which was separated using the Dean Stark trap. The rheostat energy was increased to increase the collection rate of the liquid and 15 ml of ethanol was recovered in the trap. The product was distilled under vacuum and two fractions were taken, one at 80-90°C at 20 torr (probably unreacted starting materials) and the other at 90-100°C at 20 torr. H 1 NMR of the fraction boiling at 90-100°C showed only a small amount of product formed. The latter fraction probably contained largely unreacted starting material.

Example IX

Acetic acid (30.6 g) was placed in a 250 ml round bottom flask. Ethylenediamine (30 g) was added dropwise over a period of 25 minutes while the mixture was cooled externally in an ice bath. At this point a light golden brown solid formed. The mixture was then heated to 230°C and 18 ml of water distilled off. The sample was then transferred to a smaller round bottom flask and distilled in vacuo until the temperature in the flask reached 180°C, at which point a white crystalline substance had sublimed and plugged the condenser. Distillation was therefore discontinued. A small amount of the cooled material was then placed in the sublimation apparatus under vacuum and in a hot water bath. A small amount of pure material sublimed.

Example X

Acetic acid (30.6 g) was placed in a 250 ml round bottom flask. Propanediamine was added (dropwise to control the exothermic reaction) over a period of 20 minutes. The reaction mixture was cooled externally, but this caused it to solidify. It was therefore stirred at room temperature for approx. 1 hour and the sample was left overnight. It was then heated to 130°C for 8 hours until the water condensed off. About. 16.5 ml of water was distilled off and the temperature in the flask increased to 140°C. The sample was then distilled under vacuum and with hot water condenser to obtain a white solid. Fractions were taken out at 80°C and 0.5 torr and at 90 - 100°C and 0.5 torr. The first fraction probably contained an impure mixture of side reactions plus a small amount of amidine.

Example XI

Various amounts of the amidines prepared in Examples I

- X was added to light cycle gas/oil (LCGO) and to kerosene (KERO) containing different amounts of hydrogen sulphide. The hydrogen sulfide in the sample after the addition was measured, and the resulting decrease in hydrogen sulfide concentration was calculated accordingly. More specifically, for each test a sample (50 ml) of the fuel to be tested was placed in a 59 ml bottle. The bottle was capped and heated to 37.8°C for 30 minutes in an oven. A desired amount of the additive to be tested was then placed in the bottle and the bottle was shaken for 30 seconds. A known amount of hydrogen sulphide was

then quickly added to the fuel using an acidic kerosene solution (typically 30 - 50 µl of a saturated solution of hydrogen sulfide in kerosene) and the bottle was recapped and returned to the furnace. After one hour, the sample was taken out of the oven, shaken for 30 seconds and poured into the rinse test chamber. Then the sample was flushed with nitrogen (100 cm<3>/min.) for at least 30 minutes or until discoloration of the detector tube

could not be seen for 5 minutes. The hydrogen sulphide concentration in the liquid phase was measured. These results were compared with various other additives, tested using the same method and identified in the following chart:

The results are shown in the following tables:

Example XII

Further tests were carried out according to the procedure in Example XI, but with residual oil from Arco Petroleum and with the additives designated as SB4 and SB11 in Example XI, the additive from Example VI and the following two additives:

The initial H2S concentration was 1000 ppm. The following results were obtained.

Claims (10)

1. Method for removing or reducing hydrogen sulfide in an aqueous medium and/or a hydrocarbon medium, characterized in that it comprises bringing the medium into contact with an effective amount of an amidine selected from the group consisting of monoamidines with from 1 to approx. 18 carbon atoms and polyamidines comprising from 2 to 3 amidine groups with from 1 to approx. 18 carbon atoms per amidine group. 2. Method according to claim 1, characterized in that the amidine is one of the mono-amidine compounds corresponding to the formulas where R, R<1>, R<2> and R<3> are independently selected from H, alkyl groups with up to approx. 18 carbon atoms and aryl groups with up to approx. 18 carbon atoms, and where R<4> is an alkylene group with up to approx. 18 carbon atoms, provided that the total number of carbon atoms in R, R<1>, R<2>, R<3> and R<4> present in the compound is from 1 to about 18. 3. Method according to claim 1, characterized in that the amidine is a polyamidine corresponding to the formula A1_R5_A2 or where A<1>, A<2> and A<3> are independently selected from where R, Rl^R<2>Qg R<3> of each of A1, A<2> and A<3> independently selected from H, alkyl groups of up to 18 carbon atoms and aryl groups of up to 18 carbon atoms, and R<4> in each of A<1>, A<2> and A<3> is independently selected from alkylene groups of up to 18 carbon atoms, on the condition that the total number of carbon atoms in R<1>, R2, R3 and R<4> per A is from 1 to approx. 18; R<5> is an alkylene group of up to 6 carbon atoms or an arylene group of up to 6 carbon atoms, and R<6> is an alkylene group of up to 10 carbon atoms or an arylene group of up to approx. 10 carbon atoms. 4. Method according to claim 1, characterized in that the amidine has a pKa value of at least approx. 5. 5. Method according to claim 4, characterized in that the amidine has a pKa value of at least approx. 10. 6. Method according to claim 2, characterized in that R<1> is independently selected from the group consisting of hydrogen and aryl groups.' 7. Method according to claim 6, characterized in that R<1> is an aryl group. 8. Method according to claim 7, characterized in that R<1> is an aryl group which is substituted with an electron-withdrawing group. 9. Method according to claim 2, characterized in that R, R<1>, R<2> and R<3> are independently selected from lower alkyl groups, hydrogen and cycloalkyl groups. 10. Method according to claim 8, characterized in that R, R<2> and R<3> are independently selected from the group consisting of cyclic groups and alkenyl amines.